The rhesus monkey analogue of human lymphocyte antigen-G is expressed primarily in villous syncytiotrophoblasts

The human placenta expresses the nonclassical major histocompatibility complex (MHC) class I molecule, human lymphocyte antigen (HLA)-G, which may contribute to the establishment of maternal-fetal immune tolerance, Although the HLA-G ortholog of the rhesus monkey, Mamu-G is a pseudogene, another nonclassical MHC class I locus, Mamu-AG, is expressed in the rhesus monkey placenta. Mamu-AG encodes MHC class I A locus-related molecules that exhibit all the characteristics of human HLA-C, including limited polymorphism and a truncated cytoplasmic domain. We have examined MHC class I glycoprotein and Mamu-AG mRNA expression in the rhesus placenta and in cultured trophoblasts, Immunocytochemical analysis of rhesus placental tissues with the W6/32 monoclonal antibody demonstrated a high level of MHC class I expression in villous syncytiotrophoblasts, whereas villous cytotrophoblasts were largely MHC class I negative, Only law levels of MHC class I expression were seen int extravillous cytotrophoblasts of cell columns acid the trophoblastic shell, In situ hybridization demonstrated that Mamu-AG mRNAs were expressed at a high level in first-trimester villous syncytiotrophoblasts. MMC class I and Mamu-AG expression was significantly up-regulated during in vitro culture and differentiation of freshly isolated villous cytotrophoblasts into syncytiotrophoblasts. Preferential Mamu-AG expression in syncytiotrophoblasts suggests that rhesus monkey MHC class I-bearing trophoblasts could potentially interact with maternal peripheral blood lymphocytes rather than with uterine decidual lymphocytes as has been proposed for human trophoblasts.